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131.
Nitrous oxide (N2O) release by Streptomyces nitrosporeus in a sandy loam soil as affected by pO2, pH and amount of easily decomposable organic carbon In model experiments under defined conditions (80%WHC, 300 μg nitrate-N g?1 dry soil, 30°C) the effect of pO2, pH and addition of easily decomposable organic matter on nitrous oxide production by Streptomyces nitrosporeus DSM 40023 from a sterilized sandy loam soil was studied. This streptomycete reduces nitrate to N2O but not to N2. The strain was inoculated into a sterilized sandy loam soil (pH 6), enriched with nitrate and incubated at approximately 20 and 10% (v/v) O2 for 26 days. In another series of experiments the pH was increased with NaOH-solution up to pH 7 or the soil was enriched with pulverized leaves (1%) to increase mineralization activity and the demand for electron acceptors. In the headspace the concentration of O2, CO2 and N2O was analysed by GC. The soil concentration of NO3?, NO2? and NH4+ was measured as well as the pH value. The population density was determined by the plate count method. At a decreased oxygen concentration of about 2.5% (v/v) in the headspace, S. nitrosporeus increased the release of N2O. In the experiments with an initial oxygen concentration of approximately 20% (v/v) this threshold of about 2.5% /(v/v) O2 was hardly reached and consequently only little N2O was produced. Apparently, S. nitrosporeus uses O2 in preference to nitrate, which is characteristical of nitrate respiration. A pH increase from pH 6 to 7 reduced the lag phase significantly and increased the rate of oxygen consumption, CO2 release and N2O production. Maximum nitrous oxide production was reached after 13 days. The result indicated that streptomycetes like S. nitrosporeus may use nitrate alternativly to O2 to maintain energy conservation (ATP synthesis) with the release of N2O. So far, nothing is known about the role of streptomycetes in contributing to N2O production in natural soils. 相似文献
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134.
Effects of thiopental sedation on learning and memory 总被引:1,自引:0,他引:1
A G Osborn J P Bunker L M Cooper G S Frank E R Hilgard 《Science (New York, N.Y.)》1967,157(788):574-576
Subjects who were administered thiopental showed a loss of memory for events discussed while they were under sedation. We tested the subjects for recognition memory of pictures and recall of associated pairs of letters and words, and found that the subsequent memory loss was correlated with the concentration of thiopental in the venous blood at the time the material was learned. Retention did not appear to be state-dependent because the subject, while under sedation, could recall material learned prior to sedation, and because recall was not facilitated by reinstatement of the sedation. 相似文献
135.
Frank P 《Science (New York, N.Y.)》1954,119(3102):823-824
136.
Frank L 《Science (New York, N.Y.)》2000,289(5476):26-27
137.
138.
Min JH Yang H Ivan M Gertler F Kaelin WG Pavletich NP 《Science (New York, N.Y.)》2002,296(5574):1886-1889
The ubiquitination of the hypoxia-inducible factor (HIF) by the von Hippel-Lindau tumor suppressor (pVHL) plays a central role in the cellular response to changes in oxygen availability. pVHL binds to HIF only when a conserved proline in HIF is hydroxylated, a modification that is oxygen-dependent. The 1.85 angstrom structure of a 20-residue HIF-1alpha peptide-pVHL-ElonginB-ElonginC complex shows that HIF-1alpha binds to pVHL in an extended beta strand-like conformation. The hydroxyproline inserts into a gap in the pVHL hydrophobic core, at a site that is a hotspot for tumorigenic mutations, with its 4-hydroxyl group recognized by buried serine and histidine residues. Although the beta sheet-like interactions contribute to the stability of the complex, the hydroxyproline contacts are central to the strict specificity characteristic of signaling. 相似文献
139.
The numbers of rat glossopharyngeal and chorda tympani fibers responding to one, two, three, or four taste stimuli of different quality (sodium chloride, hydrochloric acid, quinine, and sucrose) and to each of the six possible pairs of these stimuli can be predicted if there are four independent sensitivities randomly distributed among innervating fibers. 相似文献
140.
Action spectra were determined for lightinduced phase shifts of the circadian rhythm of adult emergence in Drosophila pseudoobscura. The action spectra for advance and delay phase shifts are similar; the most effective wavelengths are in the blue region, with a sharp cutoff above 500 nanometers. This similarity suggests that the same photoreceptive pigment mediates both advance and delay phase shifts. 相似文献